1. Technical Field
The present invention relates to a force detection device, a robot, and a moving object.
2. Related Art
In recent years, for the purpose of an improvement in production efficiency, the introduction of industrial robots to production facilities such as a factory has progressed. Such industrial robots include an arm capable of being driven in one-axis or plural-axis directions, and an end effector, such as a hand, a component inspection instrument or a component transport instrument, which is installed at the tip side of the arm, and can execute component assembly work, component manufacturing work such as component machining work, component transport work, component inspection work, and the like.
In such industrial robots, a force detection device is provided between the arm and the end effector. As a force detection device used in the industrial robots, for example, a force detection device disclosed in JP-A-5-95237 is used. The force detection device of JP-A-5-95237 is constituted by a charge output element that outputs charge in accordance with a received external force, an amplifier that amplifies the charge which is output from the charge output element, a capacitor for converting the charge which is output from the charge output element into a voltage, and a reset circuit having a mechanical relay for short-circuiting terminals of the capacitor and resetting charge accumulated in the capacitor. With such a configuration, the force detection device of JP-A-5-95237 can detect an external force applied along any one axis to the charge output element.
However, in order to control the end effector of the industrial robot, it may be necessary to detect six-axis forces (translational force components in the directions of x, y, and z axes and rotational force components around the x, y, and z axes). In such a case, it is necessary to form a three-axis force detection device capable of detecting three-axis forces (translational forces in the directions of the x, y, and z axes) by combining at least three force detection devices as disclosed in JP-A-5-95237, and to mount at least three three-axis force detection devices to the wrist of the industrial robot.
When the size of the force detection device mounted to the wrist of such an industrial robot is large, the operating area of the wrist may become narrower. In addition, when the size of the force detection device is large, the distance from the joint of the industrial robot to the end of the end effector becomes longer, and thus the load capacity of the industrial robot may be reduced. Therefore, it is preferable that the force detection device is small in size and light in weight.
In order to solve such problems, various methods are proposed. For example, JP-A-11-148878 discloses a force detection device using a semiconductor switching element as a reset circuit. Since the semiconductor switching element is smaller in size and lighter in weight than the mechanical relay, it is possible to reduce the size and weight of the entire device by using the semiconductor switching element as the reset circuit.
However, when the semiconductor switching element is used as the reset circuit, an output drift due to a leakage current of the semiconductor switching element is generated. Such an output drift deteriorates the detection resolution and detection accuracy of the force detection device, which leads to undesirable results. Further, since the output drift is accumulated in proportion to the measurement (operating) time of the force detection device, there is a problem in that the measurable time of the force detection device cannot be lengthened.
In addition, as the force detection device, a quartz crystal piezoelectric sensor using quartz crystal as a charge output element is widely used. The quartz crystal piezoelectric sensor has characteristics excellent in a wide dynamic range, high rigidity, high natural frequency, and high load bearing capacity, and thus is widely used in the industrial robot.
However, in such a quartz crystal piezoelectric sensor, charge which is output from quartz crystal is weak, and thus it is not possible to ignore the influence of an output drift caused by the leakage current of a conversion and output circuit. Various methods for reducing the output drift have been examined. For example, JP-A-9-72757 discloses a quartz crystal piezoelectric sensor provided with a reverse bias circuit using a diode having current characteristics similar to the characteristics of the leakage current of the conversion and output circuit. In the quartz crystal piezoelectric sensor disclosed in JP-A-9-72757, a correction current which has a size substantially equal to that of the leakage current of the conversion and output circuit and of which the flow direction is opposite thereto is supplied from the diode, and thus an output drift is reduced.
However, when the reverse bias circuit is used as in the quartz crystal piezoelectric sensor disclosed in JP-A-9-72757, additional components such as the diode are required, and the mounting area thereof is expanded, which leads to the difficulty of a reduction in size. In addition, there is a problem in that component quality control for supplying a desired correction current is required.